Pressure control system for print head

ABSTRACT

A pressure controlling system for an inkjet printer includes a pressure chamber, a pump fluidically connected to the chamber and adapted for increasing or decreasing the pressure within the pressure chamber, a controllable three port two way valve, and a sensing unit including one or more pressure sensors. The pressure sensing unit is in fluidic communication with the pressure chamber for sensing the pressure therein. The valve has a first port controllably fluidically connectable to the pressure chamber, a second port controllably fluidically connectable to an inkjet print head, and a third port controllably fluidically connectable with atmospheric air. The sensing unit is adapted for sending signals representative of the pressure within the pressure chamber to at least one processor/controller. The pump and the valve are controlled by receiving control signals from the processor/controller(s). There are provided a method for operating the system and a printer including the system.

RELATED APPLICATION

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 62/439,950 filed Dec. 29, 2016, the contents ofwhich are incorporated herein by reference in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to inkjetprinters, more particularly, but not exclusively, to a system forcontrolling pressure applied to an inkjet print head.

Inkjet printing technology is currently used for many applications. Forexample, 2D inkjet printers (for printing a pattern on a page or otherflat or non-flat surfaces) is extensively used in desktop printingapplication for domestic, office, and industrial printing applications.Recently, 2D inkjet technology has been applied to printing varioustypes of entire electrical circuits and/or discrete electricalcomponents (including, electrical conductors, resistors, capacitors,transistors, diodes, and other electrical components) on selected 2Dsurfaces by using inks comprising organic materials suitable for themanufacturing of organic electronic components.

Inkjet technology may also be adapted for use in 3D printers capable ofproducing defined 3D objects. Additive manufacturing (AM) is generally aprocess in which a 3D object is manufactured utilizing a computer modelof the object. Such a process is used in various fields, such as designrelated fields for purposes of visualization, demonstration andmechanical prototyping, as well as for rapid manufacturing.

The basic operation of any AM system consists of slicing a 3D computermodel into thin cross sections, translating the result intotwo-dimensional position data and feeding the data to a controller of asystem that constructs a 3D structure in a layer-wise manner.

AM entails many different approaches to the method of fabrication,including 3D printing, e.g., 3D inkjet printing, stereolithography,laminated object manufacturing, fused deposition modeling and others.

In 3D printing processes, for example, a building material is dispensedfrom a printing block including one or more printing heads. Each of theprinting heads has a set or array of nozzles from which material can beselectively dispensed onto a printing tray to form one layer of a 3Dobject at a time. Depending on the building material, the layers maythen be cured or solidified using a suitable device also carried on theprinting block. The building material may include modeling material,which forms the object, and support material, which supports the objectas it is being built. The printing block scans the supporting structureand patterns it. Various 3D printing techniques exist and are disclosedin, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334,7,183,335 7,209,797, 7,225,045, 7,300,619, 7,364,686, 7,500,846,7,658,976, 7,962,237, 8,781,615 and 9,031,680, and U.S. ApplicationPublication Nos. 20130040091 and 20150035186, all of the same Assignee,the contents of which are incorporated herein by reference.

Inkjet print heads (of both 2D and 3D printers) have a unique set ofrequirements for proper operation. One such requirement is theapplication of negative pressure (defined herein as a pressure lowerthan the atmospheric pressure in the print head environment) to the inkinside the print head in order to avoid “weeping” of ink at the printhead nozzle orifices. Another requirement is associated with cleaningthe print head nozzle orifices in order to avoid or reduce clogging ofthe orifices and/or nozzles of the print head by debris and/orsolidified ink accumulating at such orifices/nozzles.

This may be achieved by purging the print head by temporarily applyingpositive pressure (defined herein as a pressure higher than theatmospheric pressure in the print head environment) to the ink insidethe print head. Such a pulse of positive pressure forces an amount ofink to flow from the print head's internal ink reservoir through theorifices/nozzles, which cleans the orifices/nozzles and preventsclogging. Such print head purging may be performed periodically by theprinter and/or may be performed on beginning a print job, and/or mayeven be a user initiated “on demand” purging.

The amount of ink ejected from the orifices/nozzles during such purgingaction is wasted. It is therefore desirable to perform the purging byproviding a steep step-like function increase of the inkjet print headpressure so as to minimize the time of application of positive pressureto the print head, in order to reduce the amount of ink wasted duringpurging.

When the negative pressure needs to be applied and maintained in a printhead, a low capacity pump may adequately perform such negative pressuremaintenance. However, when a positive pressure pulse or step-likefunction pressure increase is needed, it may be difficult to achieve bya low capacity pump and may therefore require the use of a moreexpensive high capacity pump.

Additionally, once the positive pressure surge has been achieved andpurging is completed, there is a need to reduce the pressure in theprint head as fast as possible to reach the operating negative pressurelevel suitable to prevent weeping. This may also be difficult to achieveswiftly enough by using a low capacity pump and may also require the useof an expensive high capacity pump.

The need for supplying variable pressure levels for performing variousactions of the print head has been addressed in different ways in priorart inkjet print heads. For example, U.S. Pat. No. 6,302,516 to Brookset al. discloses an ink supply system for an inkjet print head. The inksupply system includes a vacuum reservoir connected to a vacuum pump andto a restricted passage and a purge reservoir connected to an air pumpand another restricted passage.

Chinese Patent No. CN104626403 (A) to Huang Xiang Feng discloses alight-cured 3D printing material supply fluid path system.

Chinese Patent No. CN204095297(U) to Li Xiaoping discloses an inkviscosity self-adaptive code spraying printer.

There is an ongoing need for systems for efficiently andcost-effectively controlling the pressure applied to an inkjet printhead and for performing fast pressure changes.

SUMMARY OF THE INVENTION

The present application discloses a system for controlling the pressureapplied to a print head or print heads of an inkjet printer.

An aspect of some embodiments of the pressure control system is that thepressure control system includes a pump usable for print head purging byproducing a positive pressure in the internal ink reservoir of a print(or of multiple print heads) and for producing a negative pressurewithin the internal ink reservoir(s) of the print head(s) to avoidweeping through the print head's orifices or nozzles.

The pump fluidically communicates with a pressure chamber and thepressure chamber is in fluidic communication with a two way/three portvalve having a first port controllably fluidically connectable to thepressure chamber, a second port controllably fluidically connectable tothe print head internal ink reservoir(s) or to a print head pressuremanifold (in case of multiple print heads being connected to thepressure controlling system through a manifold) and a third portcontrollably fluidically connectable to the atmosphere surrounding theprint head(s). The pressure controlling system includes a pressuresensor unit including one or several pressure sensors. The pressuresensor unit is in fluidic communication with the pressure chamber andsenses the pressure within the pressure chamber. The pressure sensorunit is adapted for sending signals representative of the pressurewithin said pressure chamber to at least one processor/controller, andthe pump is adapted to receive control signals from theprocessor/controller(s) for controlling the operation of the pump. Thevalve is adapted for receiving control signals from theprocessor/controller(s) for controlling the operation of the valve.

In accordance with some embodiments, the processor/controller unit(s)may be at least one processor/controller included in the pressurecontrolling system and adapted to control the operation of the valve andthe pump. The processor/controller(s) may also be adapted to communicatewith at least a second processor/controller controlling the operation ofone or more print heads of the printer to receive command signals fromthe second processor/controller and (optionally) to send status signalsto the second processor/controller(s).

In accordance with some embodiments, there is at least oneprocessor/controller included in the printer that is adapted to controlthe operation of the pressure controlling system and the operation ofone or more print heads of the printer.

In accordance with some embodiments, there is a combination of at leastone processor/controller included in the pressure controlling system andat least one processor/controller included in the printer andcommunicating with the at least one processor/controller of the pressurecontrolling system. The combination is adapted for operating the pumpand the valve and for controlling the operation of one or more printheads of the printer.

In accordance with some embodiments of the pressure controlling system,the pressure controlling system also includes a filter fluidicallyconnected between the pump and the atmospheric air for filtering airentering the pump.

In accordance with some embodiments of the pressure controlling system,the second port of the valve is fluidically connected to one or moreinkjet print heads by a hollow conduit for controlling the pressurewithin the print head(s) and the pressure controlling system alsoincludes an ink backflow detecting sensor for detecting backflow of inkfrom the inkjet print head(s) through the hollow conduit before the inkenters the second port.

In accordance with some embodiments of the pressure controlling system,the hollow conduit is a transparent hollow conduit and the ink backflowdetecting sensor is an optical sensor.

In accordance with some embodiments of the pressure controlling system,the pump is a reversible peristaltic pump which may pump air into or outof the pressure chamber.

In accordance with some embodiments of the pressure controlling system,the pump includes a stepper motor.

In accordance with some embodiments of the pressure controlling system,the pressure sensing unit may be a pressure sensing unit disposed withinthe pressure chamber, and

In accordance with some embodiments of the pressure controlling system,the pressure sensing unit is a pressure sensing unit disposed outsidethe pressure chamber and fluidically connected to the pressure chamberthrough one or more hollow conduits connected to the pressure sensor(s).

In accordance with some embodiments of the pressure controlling system,the pressure sensing unit includes multiple pressure sensors, eachpressure sensor of the multiple pressure sensors is adapted for sensingpressure in a sub-range of the full range of pressures achievable withinthe pressure chamber for increasing the dynamic range and/or theresolution of the pressure sensing unit.

In accordance with some embodiments of the pressure controlling system,the three port two way valve is a solenoid valve.

In accordance with some embodiments of the pressure control system, thepump is a bidirectional or reversible pump capable of pumping a fluid orgas in two opposite directions.

In accordance with some embodiments of the pressure control system, theperistaltic pump is a variable speed pump.

The present application also provides an inkjet printer including thepressure controlling system as disclosed herein and at least onecontrollably movable inkjet print head. The print head(s) is/arefluidically connected to the pressure controlling system for controllingthe pressure level within at least one internal ink reservoir disposedwithin said print head(s).

In accordance with some embodiments of the printer, the at least oneprocessor/controller of the pressure controlling unit is at least oneprocessor/controller included in the pressure controlling system andadapted to control the operation of the valve and of the pump. The atleast one processor/controller is also adapted to communicate with atleast a second processor/controller controlling the operation of atleast one print head of the printer, for receiving command signals fromthe at least second processor/controller and for (optionally) sendingstatus signals to said at least second processor/controller.

In accordance with some embodiments of the printer, the at least oneprocessor/controller is included in the printer and is adapted tocontrol the operation of the pressure controlling system and to controlthe operation of the at least one print head of the printer.

In accordance with some embodiments of the printer, the printer includesa combination of at least one processor/controller included in saidpressure controlling system and at least one processor/controllerincluded in the printer and communicating with the at least oneprocessor/controller of the pressure controlling system. The combinationis adapted for operating the pump and the valve and for controlling theoperation of the at least one print head of the printer.

In accordance with some embodiments of the printer, the pressurecontrolling system also includes a filter fluidically connected betweenthe pump and the atmospheric air for filtering air entering the pump.

In accordance with some embodiments of the printer, the second port ofthe valve is fluidically connected to the at least one inkjet print headby a hollow conduit for controlling the pressure within the at least oneprint head and the pressure controlling system also includes an inkbackflow detecting sensor for detecting backflow of ink from the atleast one inkjet print head through the hollow conduit before the inkenters the second port.

In accordance with some embodiments of the printer, the hollow conduitis a transparent hollow conduit and the ink backflow detecting sensor isan optical sensor.

In accordance with some embodiments of the printer, the pump is areversible peristaltic pump.

In accordance with some embodiments of the printer, the pump includes astepper motor.

In accordance with some embodiments of the printer, the pressure sensorunit is a pressure sensor unit disposed within the pressure chamber.

In accordance with some embodiments of the printer, the pressure sensorunit is disposed outside the pressure chamber and fluidically connectedto the pressure chamber through one or more hollow conduits connected tothe one or more pressure sensors.

In accordance with some embodiments of the printer, the pressure sensorunit includes multiple pressure sensors. Each pressure sensor of themultiple pressure sensors is adapted for sensing pressure in a sub-rangeof the full range of pressures achievable within the pressure chamberfor increasing the dynamic range and/or the resolution of the pressuresensing unit.

In accordance with some embodiments of the printer, the three port twoway valve is a solenoid valve.

In accordance with some embodiments of the printer, the pump is abidirectional or reversible pump capable of pumping a fluid or gas intwo opposite directions.

In accordance with some embodiments of the printer, the peristaltic pumpis a variable speed pump.

In accordance with some embodiments of the printer, the ink jet printeris a 2D inkjet printer or a 3D inkjet printer.

There is also provided a method for controlling pressure in a print headof an inkjet printer comprising the pressure controlling systemdisclosed herein. The method includes the steps of, receiving pressurerelated signals from the pressure sensing unit of the pressurecontrolling system, the pressure related signals represent the pressurelevel within the pressure chamber, receiving printing control signalsfor operating the print head and processing the pressure related signalsand/or the control signals to provide pump control signals to the pumpand/or valve control signals to the valve.

In accordance with some embodiments of the method, the step ofprocessing includes the steps of, receiving a vacuum mode controlsignal, closing the valve to fluidically connect the print head(s) tothe atmosphere and to disconnect the pressure chamber from theatmosphere, operating the pump to reduce the pressure within thepressure chamber to a vacuum mode pressure level, and opening the valveto fluidically connect the print head(s) to the pressure chamber.

In accordance with some embodiments of the method, the vacuum modepressure level is a set or preset pressure value.

In accordance with some embodiments of the method, the step of operatingthe pump includes the step of closing the valve to allow the pressurewithin the inner spaces of the print block (or print blocks if there aremore than one print block) to equilibrate with atmospheric pressureprior to the step of operating said pump.

In accordance with some embodiments of the method, the step ofprocessing includes, receiving a purging control signal for performingpurging of the print head(s), closing the valve to allow the pressurewithin the print head(s) to equilibrate with atmospheric pressure,operating the pump to increase the pressure within the pressure chamberto a purge pressure level, and opening the valve to fluidicallydisconnect the print head(s) from the atmosphere and to fluidicallyconnect the pressure chamber to the print head(s), for purging the printhead(s).

In accordance with some embodiments of the method, the purge pressurevalue is a set or preset value.

In accordance with some embodiments of the method, the vacuum pressurevalue and the purge pressure value are determined from the volume withinthe pressure controlling system and the total volume included within theprint head(s) and the hollow conduit(s) connecting the print head(s) tothe pressure controlling system.

In accordance with some embodiments of the method, the vacuum pressurevalue and the purge pressure value are determined and set for eachdifferent combination of the pressure controlling system and one or moreprint heads.

In accordance with some embodiments of the method, the step ofprocessing also includes reversing the direction of pumping of the pumpafter the purging is completed to reduce the pressure within thepressure chamber to a level equal to or smaller than the vacuum modepressure level.

In accordance with some embodiments of the method, the step ofprocessing also includes the step of checking if ink backflow isdetected and if ink backflow has been detected operating the pump toincrease pressure within the pressure chamber for preventing ink fromentering the pressure controlling system.

In accordance with some embodiments of the method, the step of checkingalso includes the step of disabling the pump after preventing ink fromentering the pressure controlling system.

In accordance with some embodiments of the method, the step of checkingalso includes the step of outputting an ink backflow message.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention may involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions.

Optionally, the data processor includes a volatile memory for storinginstructions and/or data and/or a non-volatile storage, for example, amagnetic hard-disk and/or removable media, for storing instructionsand/or data. Optionally, a network connection is provided as well. Adisplay and/or a user input device such as a keyboard or mouse areoptionally provided as well.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawing, in which likecomponents are designated by like reference numerals. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings (in which like components aredesignated by like reference numbers) makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a schematic diagram illustrating a pressure controlling systemin accordance with an embodiment of the pressure controlling systems ofthe present application;

FIG. 2 is a schematic diagram illustrating a pressure controlling systemin accordance with another embodiment of the pressure controllingsystems of the present application;

FIG. 3 is a schematic diagram illustrating part of an inkjet printerincluding a pressure controlling system fluidically connected to aninkjet print head of the inkjet printer, in accordance with someembodiments of the inkjet printers of the present application;

FIG. 4 is a schematic isometric view illustrating a pressure controllingsystem in accordance with an exemplary embodiment of the pressurecontrolling systems of the present application;

FIG. 5 is a schematic side view of the pressure controlling system ofFIG. 4;

FIG. 6 is a schematic isometric view of part of the pressure controllingsystem of FIG. 4;

FIG. 7 is a schematic, part cross sectional part fluidics block diagramillustrating a multiple print head printing block of a 3D inkjet printerconnected to a pressure controlling system, in accordance with anembodiment of the inkjet printers of the present application;

FIG. 8 is a schematic part fluidic/part block diagram illustrating aninkjet printer using a pressure control system in accordance with yetanother embodiment of the pressure control system and of the inkjetprinters of the present application;

FIG. 9 is a schematic flow chart illustrating the steps of a method ofoperating a pressure controlling system in a printer, in accordance withsome embodiments of the methods of the present application; and

FIGS. 10A-10B are schematic flow charts illustrating the steps of amethod of operating a pressure controlling system in a printer, inaccordance with some embodiments of the methods of the presentapplication.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

Abbreviations:

The following abbreviations are used throughout the present application:

AM=Additive manufacturing.

ATM=Atmosphere (pressure unit).

2D=two dimensional.

3D=three dimensional.

DSP=Digital signal processor.

DOD=Drop on demand.

IC=Integrated circuit.

mm=millimeter.

NO 3/2 valve=normally open three port two way valve.

NC 3/2 valve=normally closed three port two way valve.

PCB=Printed circuit board.

PSI=Pounds per square inch.

SEC=Seconds.

S/N=Signal to noise ratio.

TTL=Transistor Transistor Logic.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

It is expected that during the life of a patent maturing from thisapplication many relevant devices and systems for pumping fluids will bedeveloped and the scope of the terms “pump” and “pumps” are intended toinclude all such new technologies a priori. It is also expected thatduring the life of a patent maturing from this application many relevantinkjet print heads for printing will be developed and the scope of theterms “print head”, Print heads “inkjet print head” and “inkjet printheads” are intended to include all such new technologies a priori.

As used herein the term “about” refers to ±10%.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration.” Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments.” Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

Reference is now made to FIG. 1, which is a schematic diagramillustrating a pressure controlling system in accordance with anembodiment of the pressure controlling systems of the presentapplication. The pressure controlling system 10 includes a pressurechamber 2, a three port/two way valve 4, a filter 6, a bidirectional(reversible) pump 8 having a first pump port 8A and a second pump port8B, a pressure sensor unit 12 and a processor/controller 14. Thepressure sensor unit 12 is disposed within the pressure chamber 2 forsensing the pressure within the pressure chamber 2. The pressure sensorunit 12 may include one or more pressure sensors (not shown in detail inFIG. 1 for the sake of clarity of illustration).

The pressure chamber 2 is fluidically connected to the pump 8 through afilter 6 which is interposed between the pressure chamber 2 and the pump8. The filter 6 is fluidically connected to the second pump port 8B by ahollow conduit 6A. The filter 6 is fluidically connected to the pressurechamber 2 by a hollow conduit 6B. The pump 8 has a first pump port 8Awhich opens to the atmospheric air outside the pressure controllingsystem 10 and a second pump port 8B which is connected to the filter 6and fluidically communicates with the pressure chamber 2 through thefilter 6.

The filter 6 is a filter adapted for filtering the external atmosphericair which enters the pump 8 through the first pump port 8A. The filter 6removes dust or any other particulate matter or moisture droplets or anyother contaminants from the air entering through the first pump port 8Aof the pump 8 to reduce the amount of contaminants entering the volumeenclosed within the pressure chamber 2 which reduces clogging of any ofthe fluidic passages of the pressure controlling system 10 and alsoreduces carryover of any such contaminants into any print headfluidically connected to the system 10. The pressure chamber 2 is alsoconnected to the valve 4.

The valve 4 has three ports. A first port 4A of the valve 4 iscontrollably fluidically connectable to the pressure chamber 2. A secondport 4B of the valve 4 is controllably fluidically connectable to aninkjet print head (the print head is not shown in FIG. 1 but see FIGS. 3and 4 hereinafter). A third port 4C of the valve 4 is controllablyfluidically connectable with atmospheric air. The three port/two wayvalve 4 may be any suitable type of controllable three port two wayvalve known in the art, such as, for example, a three port/two waynormally open solenoid valve. In FIG. 1, the valve 4 is implemented as anormally open three port two way valve (NO 3/2 valve), and isillustrated in the open state (when the valve 4 is de-energized). In theopen state, the valve 4 fluidically connects between the first port 4Aand the second port 4B and fluidically disconnects the third port 4Cfrom the atmospheric air. In the open state, a print head (not shown inFIG. 1) connected to the port 4B is in fluidic communication with thepressure chamber 2.

In the closed state of the valve 4 when the valve 4 is energized (notshown in FIG. 1), the second port 4B is fluidically disconnected fromthe first port 4A and the first port 4A is fluidically connected to thethird port 4C. In the closed state of the valve 4, a print head (notshown in FIG. 1) connected to the second port 4B of the valve 4 isfluidically disconnected from the pressure chamber 2 and is fluidicallyconnected to the atmospheric air through the third port 4C, resulting ina fast increase of the pressure inside the print head to atmosphericpressure.

The pump 8 may be operated in two different operational modes. In afirst operational mode (vacuum mode), the pump 8 is operated to withdrawthe air from the vacuum chamber such that the air in the pressurechamber 2 is pumped out of the pressure chamber 2 through the filter 6and the port 8B into the pump 8 and out of the port 8A out into theatmosphere. In this mode of operation, the pump 8 reduces the pressurewithin the pressure chamber 2 resulting in a partial vacuum (negativepressure) within the pressure chamber 2. If the valve 4 is in the openstate, the pressure within a print head fluidically connected to thesecond port 4B will also be a negative pressure. In the firstoperational mode (vacuum mode), when the valve 4 is in the open state,the pump 8 may be operated at a low speed to maintain the negativepressure at a relatively stable negative pressure level for avoidingweep at the orifices of the print head.

In a second operational mode (purging mode), the pump 8 is operated topump atmospheric air from the atmosphere through the port 8A into thesecond pump port 8B and through the filter 6 into the pressure chamber2. In the purging mode of operation, the pump 8 increases the pressurewithin the pressure chamber 2 to reach a pressure level which is largerthan the atmospheric pressure level. Typically, during the initial partof the purging mode, the valve 4 is in the closed state such that thepressure chamber 2 is fluidically disconnected from the print head, andthe print head is fluidically connected to the atmospheric air throughthe third port 4C. The pump 8 may then be operated at a high speed toraise the pressure within the pressure chamber to a preset purgingpressure which is larger than the atmospheric pressure.

The exact value of the preset purging pressure to be achieved within thepressure chamber 2 is determined, inter alia, by the internal volume ofspace within the specific print head or print heads that are connectedto the pressure controlling system 10 and by the ratio of the volumewithin the print head(s) to the volume of the pressure chamber 2, aswill be disclosed in more detail hereinafter. Once the pressure withinthe pressure chamber 2 has reached the preset purging pressure, thevalve 4 may be opened to fluidically connect the pressure chamber 2 withthe print head(s) (while at the same time fluidically disconnecting theprint head(s) from the atmosphere) to perform the purging of the printhead(s). After the valve 4 is opened, the pump 8 may be operated at highspeed to maintain the purging pressure for a preset period of timesufficient to perform the purging.

It will be appreciated that the closing of the valve 4 for performingpurging results in a more rapid pressure increase in the print head,because the time required for pressure equalization of the head(s) withatmospheric pressure is substantially shorter than the time it wouldhave taken the low capacity pump 8 had it been operated to pump air intothe pressure chamber 2 without closing the valve 4 to reach atmosphericpressure within the total combined volume within the print head(s) andthe pressure chamber 2. Additionally, since after closing of the valve4, the pump 8 has to raise the pressure to the desired purging pressureonly within the internal volume of the pressure chamber and since thepump 8 may continue to operate at maximal speed after the valve 4 isopened again to perform purging, the total time needed to reach therequired purging pressure within the print head(s) is reduced (ascompared to the time required to reach the same required purgingpressure had the pump been operated to increase pressure in the printhead(s) without closing the valve 4). This advantageously results in afaster rate of pressure increase which results in a steeper, faster andmore “step-like” function of the pressure increase as a function oftime.

After purging is completed, the valve 4 may be closed again tofluidically disconnect the print head(s) from the pressure chamber 2 andto fluidically connect the print head(s) to atmospheric air resulting inthe pressure within the printing head(s) equalizing with atmosphericpressure through the third port 4C. At this stage the printer mayperform a wiping of the print head(s)′ orifice plate to clean theorifice plate after purging by using any wiping method or wipingmechanism as is well known in the art of inkjet printing.

It is noted that the wiping of the orifice plate of inkjet print head ispreferably performed when the pressure within the internal inkreservoir(s) of the print head(s) is at atmospheric pressure in order toefficiently wipe the orifice plate. If wiping is performed while thepressure within the internal ink reservoirs of the print head(s) ishigher than atmospheric pressure, ink may still be pushed through theorifices resulting in ink smearing and a less efficient wiping. Ifwiping is performed when the pressure within the internal inkreservoir(s) of the print head(s) is negative (i.e. is lower than theatmospheric pressure some of the ink purged from the orifices as well asparticulate matter adhering to the surface of the orifice plate may besucked into the orifices by the wiping action which may result inorifice clogging. Thus, when wiping the orifice plate(s) with the printblock at atmospheric pressure sucking back the ink drop(s) to the printhead with any particulate matter or potential orifice clogging withdebris expelled from the orifices during the purging is prevented orreduced.

It is noted that the closing of the valve 4 results in rapid reaching ofatmospheric pressure within the internal cavities and/or passages of theprint head (such as, for example, internal ink reservoir(s) and or anymanifolds attached thereto, for more details see FIG. 7 hereinafter)which advantageously allows the rapid performing of wiping of the printhead under atmospheric pressure (as compared to the slower reaching ofatmospheric pressure in prior art systems). Therefore, the valveconfiguration disclosed in the pressure controlling systems of thepresent application may be advantageously used to rapidly dissipate thepurging pressure from the print head(s) after purging by venting thepressurized air from the printing head(s) into the atmosphere throughthe third port 4C of the valve 4 as disclosed hereinabove, whichadvantageously allows faster performing of wiping of the orifice plateof the print head(s) under proper pressure conditions for wiping.

After closing the valve 4 to perform the wiping, the pump 8 may beactivated in the first mode (vacuum mode) to lower the pressure withinthe pressure chamber 2 to produce and maintain a negative pressurewithin the pressure chamber 2 while the print head(s) are being wiped.This advantageously utilizes the time period required for wiping toenable a faster return to the negative pressure required for printing(as compared to a hypothetical situation in which the pump 8 may havebeen operated to reduce the pressure within the combined volumes of thepressure chamber 2 and of the print head(s) after wiping is completedand the valve 4 being opened after print head wiping is completed). Thisfaster return to the operating negative pressure level reduces the printhead(s)′ idle time and advantageously improves the overall printingspeed.

The controlling of the operation of the pressure controlling systems ofthe present application is typically performed by one or moreprocessor/controllers. In the exemplary embodiment of the pressurecontroller system 10, the processor/controller 14 that controls theoperation is implemented as a dedicated processor/controller which is adedicated processor/controller physically disposed (together with anyassociated electronic circuitry) on or in the pressure controllingsystem 10. The processor/controller 14 may be any type of processingand/or controlling unit known in the art.

For example, the processor/controller unit may be a microprocessor, amicrocomputer, a digital signal processor (DSP), a microcontroller, orany other type of device capable of receiving and processing data fromsensors or from any other devices, receiving command and/or controlsignals from other devices (such as, for example, from anothercontroller/processor(s) and outputting control and/or command signals toother device (such as, for example, the valve 4 and the pump 8)). Theprocessor/controller 14 may be a digital device or an analog device or ahybrid analog/digital device, as is known in the art. Theprocessor/controller 14 may be an integrated circuit (IC) and may beimplemented to include any required discrete or integrated supportcircuitry disposed within or outside of the inkjet printer) as is knownin the art. For example, the processor/controller 14 may be suitablyincluded in a printed circuit board (PCB) (not shown in FIG. 1 for thesake of clarity of illustration, but see FIG. 5 hereinafter). Theprocessor/controller 14 may also include any type of memory device(s)necessary for storing data, if such data storage is required foroperating.

The processor/controller 14 is suitably electrically coupled to anypressure sensor(s) included in the pressure sensor unit 12 and isconfigured to receive from the pressure sensor(s) signal representingthe pressure within the pressure chamber 2. It is noted that theindividual pressure sensors included in the pressure sensor unit 12 arenot shown in detail in FIG. 1 for the sake of clarity of illustration.The processor/controller 14 is also electrically connected to the pump 8and may send to the pump 8 pump control signals for controlling theoperation thereof. The pump control signals may control the direction ofpumping (either pumping air into the pressure chamber 2 to increase thepressure within the pressure chamber 2 or pumping air out of thepressure chamber 2 to reduce the pressure therein) and/or the rate ofpumping of the pump 8.

The processor/controller 14 is also suitably electrically connected tothe valve 4 for controlling the operation thereof. In the exemplaryembodiment of the pressure control system 10 of FIG. 1, in which thevalve 4 is a NO3/2 valve, the control signals may include an energizingsignal applying a suitable voltage to the electrical terminals of thevalve 4 for closing the valve 4 to switch the valve 4 into the closedstate and not applying any voltage to the terminals of the valve 4 inorder to maintain the valve 4 in the open state (the open and closedstates of the valve 4 may be as disclosed in detail hereinabove).

The processor/controller 14 may be suitably connected to aprocessor/controller (not shown in FIG. 1) operating the printer withinwhich the pressure controlling system 10 is included by a communicationline 15, for receiving command signals from the printer'sprocessor/controller. Typically, such command signals may include a“purge signal” instructing the pressure control system 10 to perform apurge sequence of steps required for purging the print head(s) and a“vacuum signal” instructing the pressure control system to perform asequence of steps required for returning the pressure within the printhead(s) to the negative pressure required for preventing weeping.

In some embodiments of the pressure controlling systems of the presentapplication the communication line 15 may (optionally) be abidirectional communication line for providing signals (such as statussignals) and/or data to the processor/controller (not shown in FIG. 1)operating the printer. Such data may include, among others, pressurelevel data obtained from the pressure sensor unit 12, signals or datafrom an ink backflow detector (if present, such as in the exemplaryembodiment of the pressure controlling system 30 of FIG. 3 hereinafter)or other data.

It is noted that while the exemplary embodiment of the pressurecontrolling unit 10 of FIG. 1 preferably uses a normally opened threeport two way valve, this is not obligatory and a suitable normallyclosed three port two way valve (NC 3/2 valve) may also be used withsuitable adaptation of the control software or firmware. Theconfiguration of such an embodiment using an NC 3/2 valve will beapparent to the person skilled in the art and is therefore not disclosedin detail hereinafter. Briefly, if the pressure control system uses aNC3/2 valve, the processor controller controlling the valve may apply anopening signal (such as, for example a positive voltage) in order tohold the valve in the opened state while no such signal may be requiredto maintain the valve at the closed state.

Reference is now made to FIG. 2, which is a schematic diagramillustrating a pressure controlling system in accordance with anotherembodiment of the pressure controlling systems of the presentapplication.

The pressure controlling system 20 includes a pressure chamber 3, athree port/two way valve 4, a filter 6, a bidirectional (reversible)pump 8, a pressure sensor unit 12 and a processor/controller 14. Thepressure controlling system 20 is similar in construction and operationto the system 10 of FIG. 1, except that, while in the pressurecontrolling system 10 (of FIG. 1) the pressure sensor unit 12 isdisposed within the pressure chamber 2, the pressure sensor unit 12 ofthe pressure controlling system 20 (of FIG. 2) is disposed outside ofthe pressure chamber 3 and is fluidically connected to the internalspace within the pressure chamber 3 by one or more suitable hollowconduits 5.

The pressure chamber 3 may be similar in volume and shape to thepressure chamber 2 of FIG. 1, except that it has suitable openingstherein for connecting the hollow conduit(s) 5 such that the hollowconduit(s) 5 fluidically connect any of the pressure sensor(s) of thepressure sensor unit 12 to the internal volume of the pressure chamber3. In some embodiments of the pressure controlling system 20, thepressure sensor unit 12 may include two (or, optionally, more than two)different sensors with each pressure sensor having a different pressureworking range for increasing and improving the dynamic range andsensitivity of the pressure sensor unit 12. Such an exemplary embodimentis disclosed in detail with respect to FIGS. 4-6 hereinafter.

An advantage of the configuration of the pressure controlling system 20is that it allows the use of relatively large pressure sensor(s) to beused without excessively reducing the internal volume of the pressurechamber 3. Another advantage of the configuration of the pressurecontrolling system 20 is that any pressure sensors included in thepressure sensor unit 12 may be disposed in any location in or on thesystem 20 which allows placement of such pressure sensor(s) close to theprocessor/controller 14, reducing the length of any electricalconnections from the processor/controller 14 to the sensor(s) andallowing for better shielding of any electrical pressure related signalsin such electrical connections which may improve the signal to noiseratio (S/N) of the pressure related signals. The pressure controllingsystem illustrated in FIGS. 4-5 hereinafter discloses an exemplaryembodiment of the system 20 in detail.

The construction and operation of the valve 4 the processor/controller14, the pump 8, and the filter 6 are as disclosed in detail hereinabovewith respect to the pressure controlling system 10 of FIG. 1.

The processor/controller 14 of the pressure controlling system 20 may besuitably connected to a processor/controller (not shown in FIG. 2)operating the printer within which the pressure controlling system 10 isincluded by a communication line 15, for receiving command signals fromthe printer's processor/controller. Typically, such command signals mayinclude a “purge signal” instructing the pressure control system 10 toperform a purge sequence of steps required for purging the print head(s)and a “vacuum signal” instructing the pressure control system to performa sequence of steps required for returning the pressure within the printhead(s) to the negative pressure required for preventing weeping.

In some embodiments of the pressure controlling systems of the presentapplication the communication line 15 may (optionally) be abidirectional communication line for providing signals (such as statussignals) and/or data to the processor/controller (not shown in FIG. 2)operating the printer. Such data may include, among others, pressurelevel data obtained from the pressure sensor unit 12, signals or datafrom an ink backflow detector (if present, such as in the exemplaryembodiment of the pressure controlling system 30 of FIG. 3 hereinafter)or other data.

Reference is now made to FIG. 3, which is a schematic diagramillustrating part of an inkjet printer including a pressure controllingsystem fluidically connected to an inkjet print head of the inkjetprinter, in accordance with some embodiments of the inkjet printers ofthe present application.

The inkjet printer 50 includes a pressure controlling system 30, aninkjet print head 40 fluidically connected to the pressure controllingsystem 30 by a flexible hollow conduit 40B, an (optional) ink overflowdetector 7, an external ink supply system 39 fluidically connected tothe print head 40 for supplying ink thereto and an (optional) printingtray 41. If the printer 50 is implemented as a 3D AM printer, the tray41 may be used to build the printed object thereupon.

The ink jet printer 50 also includes a processor/controller 24 and allthe necessary control electronics (not shown) and moving mechanisms (notshown) for controlling the movements of the print head 40. It is notedthat the control electronics of the printer 50 and the moving mechanismsof the print head 40 are not shown in detail in FIG. 3 for the sake ofclarity of illustration. Such control electronics and print head movingmechanisms (which may be 2D moving mechanisms or 3D moving mechanisms)are well known in the art, are not the subject matter of the presentapplication and are therefore not described in detail hereinafter.

The processor/controller 24 of the printer 50 may be connected to theprint head 40 for operating the print head 40D and may also be connectedto any print head moving mechanisms (not shown) to control the operationthereof (the communication lines connected between the processorcontroller 24 and the print head 40 and the communication line connectedbetween the processor/controller 24 and any moving mechanisms for movingthe print head 40, are not shown in FIG. 3 for the sake of clarity ofillustration). The processor/controller 24 of the printer 50 is alsoconnected to the processor/controller 14 of the pressure controllingsystem by a communication line 15 for providing command signals to theprocessor controller 14.

Typically, such command signals may include a “purge signal” instructingthe pressure control system 30 to perform a purge sequence of stepsrequired for purging the print head 40 and a “vacuum signal” instructingthe pressure control system to perform a sequence of steps required forreturning the pressure within the print head 40 to the negative pressurerequired for preventing weeping. The communication line 15 may(optionally) be a bidirectional communication line for providing signals(such as status signals) and/or data to the processor/controller 24operating the printer. Such data may include, among others, pressurelevel data obtained from the pressure sensor unit 12, signals or datafrom an ink backflow detector 7 and/or other data.

The print head 40 may include a print block 40C including an internalink reservoir 40A fluidically connected to an external ink supply system39. The internal ink reservoir 40A fluidically communicates with an inkejecting mechanism 40D. The ink ejecting mechanism 40D may be, but notlimited to, a thermal ink-drop ejecting mechanism, a piezoelectric inkdrop ejecting mechanisms or any other type of drop on demand (DOD) inkejecting mechanism known in the art. The internal ink reservoir 40A isfluidically connected to the external ink supply system 39 whichsupplies ink 43 to keep the level of ink 43 in the internal inkreservoir 40A at a substantially fixed level. The external ink supply 39may include an external ink reservoir 49 which may include an air vent49A, a pump 48 and a filter 46. The external ink reservoir 49 isfluidically connected to the pump 48 to supply the ink 43 to the pump48. The pump 48 may be fluidically connected to a filter 46 and may pumpink 43 through the filter 46 for filtering the ink 43 to remove anyparticulate matter which may clog any fluidic passages within the printhead 40 or any small passages and/or orifices in the ink ejectingmechanism 40D. The filter 46 may be suitably fluidically connected tothe internal ink reservoir 40A to supply ink 43 thereto.

The pressure controlling system 30 is similar in construction andoperation to the pressure controlling system 20 of FIG. 2, except thatit may also include an (optional) ink backflow detector 7. In accordancewith some embodiments of the pressure controlling systems of the presentapplication, the backflow detector 7 may be used to detect backflow ofink 43 through the hollow conduit 40B connecting the internal inkreservoir 40A to the third port 4B of the two way/three port valve 4.Such a backflow detector is advantageous in cases in which the inksupply system malfunctions (or received faulty control signals from anyelectrical circuitry and/or processor/controller controlling theoperation of the pump 48) causing excess ink 43 to backflow through theinternal ink reservoir 40A into the hollow conduit 40B and from thehollow conduit 40B into the valve 4. Such backflow may block thepassages within the valve 4 and may cause malfunction of the valve 4.

In some embodiments of the pressure control systems of the presentapplication, the hollow conduit 40B may be a flexible opticallytransparent hollow tubing and the backflow detector may be an activeoptical sensor including a light source (not shown) illuminating a partof the hollow conduit 40B with visible light or with any otherelectromagnetic radiation having a wavelength or wavelength range towhich the material of the hollow conduit 40B is transparent (forexample, Infrared radiation) and a light sensor (not shown) for sensingchanges in the absorption of light caused by the ink 43 flowing throughthe part of the hollow conduit 40B which is monitored by the backflowdetector 7.

The backflow detector 7 may be suitably connected to the processorcontroller 14 for providing signals representative of the absorption oflight by the monitored part of the hollow conduit 40B. If the ink 43reaches the monitored part of the hollow conduit 40B, the change inlight absorption due to the presence of ink 43 in the optical path ofthe backflow detector 7 is sensed and output to the processor/controller14. The processor/controller 14 is programmed to detect the presence ofink 43 in the monitored part of the hollow conduit 40B by processing thesignals output by the optical sensor of the backflow detector and torespond to the detection of ink backflow by sending a command to thepump 8 to operate at maximal speed to increase the pressure within thepressure chamber 3 to purging pressure level in order to push any ink inthe hollow conduit 40B back towards the internal ink reservoir 40A toavoid the ink 43 from reaching the valve 4.

It is noted that the backflow detector 7 need not obligatorily beimplemented as an optical sensor, and other types of sensors may be usedto implement the backflow detector 7. For example, in accordance withsome embodiments of the pressure controlling systems of the presentapplication, the backflow detector may be a capacitance sensor, anultrasonic sensor, an inductance sensing sensor, or any other type ofsensor/detector capable of detecting ink reaching a selected part of thehollow conduit 40B, as is known in the art. It is further noted that insome embodiments of the pressure controlling systems of the presentapplication, the processor/controller 14 may need to process signalssensed by the backflow detector to detect if ink has backflowed into thehollow conduit 40B, in some other embodiments of the pressurecontrolling systems of the present application, the backflow detector 7may include additional (analog and/or digital) electrical circuitrywhich may further process any signals sensed by any sensor(s) includedin the backflow detector 7 to autonomously detect the presence of inkbackflow (without the need for any processing by the processorcontroller 14. In such embodiments, the backflow detector 7 may outputto the processor/controller 14 a signal representing the detection ofink backflow (such as, for example, a positive going TTL voltage pulse,or, alternatively, any other type of suitable signal known in the art).

The pressure within the internal ink chamber 40A is controlled by thepressure controlling unit 30 as disclosed in detail hereinabove for thepressure controlling system 20 of FIG. 2. In embodiments including thebackflow detector 7, the processor/controller 14 (or any otherprocessor/controller included in the printer 50) may also be programmedto respond to a detection of ink backflow by operating the pump 8 toincrease the pressure level within the pressure chamber 3 to purgingpressure levels as disclosed in detail hereinabove.

It is noted that while the specific exemplary embodiment of the printer50 of FIG. 3 includes a single print head, this is not obligatory, andthe pressure controlling systems of the present application (such as,for example, the pressure controlling systems 10, 20 and 30 of FIGS. 1,2 and 3, respectively) may be included in inkjet printers (of the 2D or3D types) having multiple print heads and may be used as disclosedhereinabove to control the pressure levels within multiple print heads.

For example, the pressure controlling system 100 disclosed hereinafterwith respect to FIGS. 4-6 (as well as any of the other pressurecontrolling systems disclosed in the present application) may be used tocontrol the pressure levels in any type of printers having multipleprint heads (such as, for example the multi-print head assemblyincluding eight different print heads of FIG. 8 hereinafter). Thus, thepressure controlling systems disclosed in the present application may beused for simultaneously controlling the pressure of inkjet print headassemblies including any practical number of print heads, such as printhead assemblies including 1-32 print heads or any number of print headsgreater than 32 print heads.

It is also noted that the ink backflow detector (or ink backflow sensor)disclosed with respect to the pressure controlling system 30 of FIG. 3is not obligatory to implementing the pressure controlling systems ofthe present application and that some embodiments of the pressurecontrolling systems (such as the exemplary systems 10 and 20, disclosedhereinabove and illustrated in FIGS. 1 and 2, respectively) may beconstructed and operated without an ink backflow detector/sensor.

Reference is now made to FIGS. 4-6. FIG. 4 is a schematic isometric viewillustrating a pressure controlling system in accordance with anexemplary embodiment of the pressure controlling systems of the presentapplication. FIG. 5 is a schematic side view of the pressure controllingsystem of FIG. 4. FIG. 6 is a schematic isometric view of part of thepressure controlling system of FIG. 4.

The pressure controlling system 100 includes a pressure chamber 103, athree port/two way valve 104, a filter 106 (not seen in the particularisometric view of FIG. 4 but shown in FIG. 5), a bidirectional(reversible) pump 108, two pressure sensors 112A and 112B and aprocessor/controller 14. The pressure sensors 112A and 112B and theprocessor controller 114 are disposed on a printed circuit board 107that is attached to a mounting panel 109. The pressure sensors 112A and112B are fluidically coupled to the pressure chamber 103 by two suitableconduits 105A and 105B, respectively, for sensing the pressure withinthe pressure chamber 103. The pressure chamber 103 is fluidicallyconnected to the pump 108 through a filter 106 (best seen in FIG. 6)which is interposed between the pressure chamber 103 and the pump 108.The filter 106 is fluidically connected to the second pump port 108B bya hollow conduit 106A.

The filter 106 is fluidically connected to the pressure chamber 103 by ahollow conduit 106B. The pump 108 has a first pump port 108A which opensto the atmospheric air outside the pressure controlling system 100 and asecond pump port 108B which is connected to the filter 106 andfluidically communicates with the pressure chamber 103 through thefilter 106. The filter 106 is a filter adapted for filtering theexternal atmospheric air which enters the pump 108 through the firstpump port 108A.

The pressure chamber 103 is also connected to the valve 104. The valve104 has three ports. A first port (not shown) of the valve 104 iscontrollably fluidically connectable to the pressure chamber 103. Asecond port (not shown in the isometric view of FIG. 5) of the valve 104is controllably fluidically connected to an output fitting 104B which isconnectable to an inkjet print head (the print head is not shown inFIGS. 4-6 but see FIGS. 3, 7 and 8 illustrating print head(s) coupled tothe pressure controlling system). A third port of the valve 104 (notshown, as it is disposed at the bottom part of the valve 104) iscontrollably fluidically connectable with atmospheric air. The threeport/two way valve 104 is a model 15C1C2A4HNOAM normally open solenoidvalve, commercially available from AMISCO, Italy. The operational states(open state and closed state) of the valve 104 are as disclosed indetail hereinabove for the valve 4 of FIG. 1.

The pump 108 is a model WP11-N1/4(200)BA2G-BS material peristaltic pumpwith a ¼″ internal diameter and a BA type stepper motor, commerciallyavailable from Welco Co., Ltd., Japan. The pump 108 is powered by areversible stepper motor 108D. The pump 108 is a reversible pump andallows to pump air out of the pressure chamber 103 by rotating thestepper motor 108D in a first direction or to pump air into the pressurechamber 103 by rotating the stepper motor 108D in a second directionopposite to the first direction. The rotation speed of the stepper motor108D is also controllable by the processor controller 114 and determinesthe rate of air flow of the pump 108.

When the valve 104 is in the open state, the pump 108 may be operated intwo different operational modes. In a first operational mode (vacuummode), the pump is operated to withdraw air from the pressure chamber103 such that the air in the pressure chamber 103 is pumped out of thepressure chamber 103 through the filter 106 and the port 108B into thepump 108 and out of the port 108A out into the atmosphere.

This mode of operation of the pump 108 reduces the pressure within thepressure chamber 103 resulting in a partial vacuum within the pressurechamber 103. In a second operational mode (purging mode), the pump 108is operated to pump atmospheric air from the atmosphere through the port108A into the second pump port 108B and through the filter 106 into thepressure chamber 103. This mode of operation of the pump 108 increasesthe pressure within the pressure chamber 103.

In the exemplary embodiment of the pressure controller system 100, theprocessor/controller 114 that controls the operation of the system 100is implemented as a dedicated processor/controller which is physicallydisposed on and electrically wired to the associated electroniccircuitry on a PCB 107 that is attached to a panel 109 of the system100. The processor/controller 14 is suitably electrically coupled to thepressure sensors 112A and 112B which are also disposed on the PCB 107.The pressure sensor 112A is a model MPXV5100DP pressure sensor and thepressure sensor 112B is a model MPXV4006DP low pressure sensor bothsensors are commercially available from Freescale Semiconductor Inc.,USA. The pressure sensor 112 A is a high pressure sensor with a nominalworking pressure range of 0-14.6 ATM. The pressure sensor 112B is a lowpressure sensor with a nominal working pressure range of 0-0.87 ATM. Theuse of the two sensors 112A and 112B allows the performing of pressuremeasurements over an extended pressure range with a better dynamic rangeand sensitivity than the dynamic range and sensitivity that areobtainable by using a single pressure sensor for the entire workingpressure range of the system 100. The use of a combination of thepressure sensors 112A and 112B allows excellent dynamic range andsensitivity in a cost effective manner.

The processor controller 114 receives from the pressure sensors 112A and112B signals representing the pressure within the pressure chamber 103.The processor/controller 114 is also electrically connected to the pump108 and may send pump control signals to the pump 108 for controllingthe operation thereof. The pump control signals may control thedirection of pumping (either pumping air into the pressure chamber 103to increase the pressure within the pressure chamber 103 or pumping airout of the pressure chamber 103 to reduce the pressure therein) and/orthe rate of pumping of the pump 108.

The processor/controller 114 is also suitably electrically connected tothe valve 104 for controlling the operation thereof and for controllablyswitching the valve 104 between the open and closed states as disclosedin detail hereinabove with respect to the processor/controller 14 andthe valve 4 of FIG. 1.

Reference is now made to FIG. 6 which is a schematic side view of partof the pressure controlling system of FIG. 4.

The part of the pressure controlling system 100 illustrated in FIG. 6includes the two way/three port valve 104 fluidically connected to thepressure chamber 103, the hollow conduit 106B (used to fluidicallyconnect the pressure chamber 103 to the filter 106 of FIG. 4), theconduits 105A and 105B attached to the pressure chamber (and used tofluidically connect the pressure chamber 103 to the pressure sensors112A and 112B, respectively, of FIG. 4), and the port 104B, usable forconnecting the valve 104 to a print head (not shown in FIG. 6).

It is noted that some embodiments of the pressure controlling system 100of FIGS. 4-5, may also include an ink backflow sensor/detector (such asthe ink backflow detector 7 of FIG. 3). In accordance with one suchexemplary embodiment, the backflow detector is implemented as a tubeliquid sensor having a catalogue No. OCB350L178Z commercially availablefrom OPTEK TECHNOLOGY Inc. a TT ELECTRONICS COMPANY, TX, U.S.A. Thesensor/detector (not shown in FIG. 4 for the sake of clarity ofillustration) may be attached to the mounting panel 109 (of FIG. 4) anda transparent flexible hollow tube (not shown in FIG. 4 for the sake ofclarity of illustration) may be sealingly attached at one end thereof tothe port 104B and at the other end thereof to a print head assembly (notshown in FIG. 4, but see FIG. 8 hereinafter for an exemplary embodimentof such a print head assembly) to fluidically connect the port 104B tothe internal ink reservoir(s) of the print heads in the print headassembly.

Part of the transparent tubing connecting the print head(s) with theport 104B may pass within the detector/sensor. The detector/sensor mayoptically detect/sense any ink reaching the part of hollow tube passingthrough the detector/sensor and sends signals (detection) to theprocessor/controller 114, which, upon detection of ink backflow, mayoperate the pump 108 at maximal speed to increase the pressure withinthe pressure chamber 103 to the purging pressure level in order toprevent penetration of ink into the valve 104 and/or into any othercomponents of the pressure controlling system 100, to avoidmalfunctioning of the of the pressure controlling system 100.

Reference is now made to FIG. 7 which is a schematic, part crosssectional part fluidics, block diagram illustrating a multiple printhead assembly of a 3D inkjet printer connected to a pressure controllingsystem, in accordance with an embodiment of the inkjet printers of thepresent application.

It is noted that FIG. 7 illustrates only the components relevant tounderstanding the structure and operation of the print head assembly 170and the pressure controlling system 150 of an inkjet printer. As suchany of the other components of the printer in which the illustratedcomponents may be included, such as, for example, the printer's housingor gantry, the electromechanical systems for moving the print block 172(two dimensionally or three dimensionally) or any other mechanical,and/or electro-mechanical and/or electrical and/or electronic componentsfor supplying power and for controlling the operation of such a printerare not shown for the sake of clarity of illustration. The constructionand operation of any of the components that are not shown in FIG. 7 arewell known in the art and are therefore not discussed in detailhereinafter.

The print head assembly 170 includes a print block 172 and eight inksupply systems 139A-139H. The print block 172 includes eight print heads165A-165H and eight respective internal ink reservoirs 164A-164H. Eachof the print heads 165A-165H is fluidically connected to an internal inkreservoir of the respective internal ink reservoirs 164A-164H by ahollow passage 144 of eight hollow passages 144 formed within the printblock 172. Each of the hollow passages 144 supplies ink from an internalink reservoir to the print head associated with the internal inkreservoir. For example, the internal ink reservoir 164A supplies ink 43Ato the print head 165A through a hollow passage 144, the internal inkreservoir 164B supplies ink 43B to the print head 165B through a hollowpassage 144.

The print block 172 also includes eight hollow passages 145 formedtherein. Each of the eight hollow passages 145 is fluidically connectedat a first end thereof to a single internal ink reservoir of the eightinternal ink reservoirs 164A-164H (as illustrated in detail in FIG. 7).Each of the eight hollow passages 145 is fluidically and sealinglyconnected at a second end thereof to one of the ink supply systems139A-139H by a flexible hollow conduit 147. The eight hollow conduits147 may be any suitable flexible hollow tube made from any materialsuitable for containing inkjet ink.

Each of the eight ink supply systems 139A-139H includes an external inkreservoir 149 that is fluidically connected to a pump 148 and an inkfilter 146 that is fluidically connected to the pump 148 at its inputend and to one of the hollow conduits 147 at its output end. Theexternal ink reservoirs 149 may be vented reservoirs similar to theexternal ink reservoir 49 (of FIG. 3). Preferably, but not obligatorily,the external ink reservoirs may be replaceable cartridge type reservoirsas is known in the art.

In operation, in any one of the ink supply systems 139A-139H, the pump148 may pump ink from the external ink reservoir 149 of the ink supplysystem into the ink filter 146, to replenish the ink that is used duringprinting from the internal ink reservoir to which the specific inksupply system is fluidically connected.

In some embodiments of the print head assembly 170, each of the printheads 165A-165H is filled with a different type of ink 43A-43H,respectively. The different inks may 43A-43H may be differently coloredinks or may be any inks having different material compositions havingdifferent physical and/or chemical properties, as is well known in theart and any suitable ink combinations may be used for printing.

The printing block 172 includes a hollow manifold 162 formed therein.The hollow manifold 162 is in fluidic communication with each of theinternal ink reservoirs 164A-164H, such that the air pressure within thehollow manifold 162 and within the air space of each of the eightinternal ink reservoirs 164A-164H may equalize. The print assembly 172also includes a pressure controlling system 150. The pressurecontrolling system 150 may be fluidically connected to the print block172 by a suitable hollow conduit 160. The hollow conduit 160 may be anysuitable flexible tubing capable of withstanding the range of negativeand positive pressures produced by the pressure controlling system 150.The hollow conduit 160 is sealingly fluidically connected at a first endthereof to the hollow manifold 162 of the print block 172 and isconnected at a second end thereof to the two way/three port valve (valvenot shown in FIG. 7) of the pressure controlling system 150.

The pressure controlling system 150 may be implemented as any of thepressure controlling systems disclosed in the present application. Forexample, if the pressure controlling system 150 is implemented as any ofthe pressure controlling systems 10 or 20 or 30 (of FIGS. 1, 2 and 3,respectively), the second end of the hollow conduit 160 may be sealinglyfluidically connected to the second port 4B of the two way/three portvalve 4.

If the pressure controlling system 150 is implemented as the pressurecontrolling systems 100 (of FIGS. 4-5), the second end of the hollowconduit 160 may be sealingly fluidically connected to the second port104B of the two way/three port valve 104. Similarly, if the pressurecontrolling system 150 is implemented as the pressure controllingsystems 120 (of FIG. 8 hereinafter), the second end of the hollowconduit 160 is sealingly fluidically connected to the second port 4B ofthe two way/three port valve 4.

Returning to FIG. 7, in operation, the print head assembly 170 may beused to print either a 2D print, in the case of a 2D inkjet printer or a3D object in the case of a 3D AM inkjet printer. One of the advantagesof the pressure controlling system 150 of FIG. 7 is that it allows tosimultaneously control the pressure within the internal spaces above theinks included in all the eight internal ink reservoirs 164A-164H throughthe hollow manifold 162, obviating the need for several separatepressure controlling systems separately and individually controlling thepressure within each of the internal ink reservoirs 164A-164H.

Another advantage of the pressure control systems disclosed in thepresent application is that they allow the use of a single relativelyinexpensive low capacity reversible pump in combination with a pressurechamber and a two way three port valve to efficiently and rapidly reachthe desired negative pressure levels required to avoid weeping at theorifices of the print head(s) as well as to efficiently and rapidlyreach the positive pressure level required for purging of the printhead(s).

The use of an inexpensive low capacity pump (coupled to the pressurechamber connected to the three port two way valve) reduces the overallcost of the system as well as the overall cost of maintenance of theprinter system, reduces unnecessary waste of ink due to reducing theamount of ink wasted during the purging cycle (as the duration of thepurging cycle may be significantly reduced when using the pressurecontrol systems disclosed herein), while providing the rapid pressurechanges required by the printer between purging, wiping and printingactions, resulting in an overall reduction of purging time and of thetime required to return to the vacuum level (negative pressure) requiredfor printing, which advantageously results in faster printing rates.

This advantageous ability to rapidly reach negative and/or positivepressure levels results from the operation of the two way three portvalve as disclosed in detail hereinabove.

For example, after purging is completed, the pressure level within thepressure chamber of any of the pressure controlling systems disclosedherein is relatively high and it would have required quite a long timefor the low capacity pump of the pressure controlling system to evacuateall the air within the pressure chamber to reach the required operatingnegative pressure. However, the closing of the (normally open) valve ofthe pressure controlling systems of the present application prior tooperating the pump to reduce pressure within the pressure chamber,allows the high purging pressure within the internal volume of the printhead(s) to rapidly dissipate by equalizing with external atmosphericpressure through the third port of the two way/three port valve (suchas, for example, the third port 4C of FIGS. 1-2, or the third port ofthe valve 104 of FIG. 4).

Similarly, when purging needs to be performed while the pressure withinthe print head(s) and within the pressure chamber is negative, theclosing of the two way/three port valve allows rapid equalization of thepressure within the internal volume of the print head(s) withatmospheric pressure through the third port of the two way/three portvalve (such as, for example, the third port 4C of FIGS. 1-2, or thethird port of the valve 104 of FIG. 4) while the pump is being operatedat maximal speed to increase the pressure within the pressure chamberonly to the required purging pressure. This rapid pressure equalizationallows a shorter pumping time to reach purging pressure.

Thus, the construction and method of operation of the pressurecontrolling systems disclosed herein effectively reduce the timerequired for performing pressure transitions within printing head(s)fluidically connected to the pressure controlling system(s) betweennegative operating pressure and purging pressure and between purgingpressure to negative operating pressure. These faster pressuretransitions may reduce the print head's idle time and improve theoverall printing speed.

The inclusion of the ink backflow detectors and/or ink backflow sensors(such as, for example, the ink backflow detector 7 of FIG. 3) in someembodiments of the pressure controlling systems of the presentapplication may advantageously allow reducing or preventing entry of inkinto the components of the pressure controlling systems of the presentapplication that include such ink backflow detectors/sensors resultingin reducing printer down time, increasing the reliability of theprinter, reducing printer maintenance and reducing the cost of operationof the printer due to reduced need for replacement of pressurecontrolling systems damaged by ink backflow.

It is noted that while preferably, the pressure controlling systems mayinclude an internal processor/controller for processing signals (suchas, but not limited to, pressure related signals) and for controllingthe operation of the two way/three port valve and the pump included inthe pressure controlling system, this is not obligatory, and inaccordance with some embodiments of the pressure controlling systems ofthe present application, the pressure controlling system may be operatedby a processor/controller of a printer in which the pressure controllingsystem is disposed. Such a processor/controller of the printer may beprogrammed to control all the functions of the printer (such as, but notlimited to, print head movement control, printing head printing control,printer diagnostics, printer interface, and any other printer functions)as well as to control the operation of the pressure controlling unitinstalled in the printer.

Reference is now made to FIG. 8 which is a schematic part fluidic partblock diagram illustrating an inkjet printer using a pressure controlsystem in accordance with yet another embodiment of the pressure controlsystem and of the inkjet printers of the present application.

It is noted that FIG. 8 illustrates only the components relevant tounderstanding the structure and operation of the print head(s) 130 andthe pressure controlling system 120 of an inkjet printer 200. As such,any of the other components of the printer 200 in which the illustratedcomponents may be included, such as, for example, the printer's housingor gantry, the electromechanical systems for moving the print head(s)130 (two dimensionally or three dimensionally) or any other mechanical,and/or electro-mechanical and/or electrical and/or electronic componentsfor supplying power and for controlling the operation of the printer 200are not shown in FIG. 8, for the sake of clarity of illustration. Theconstruction and operation of any of the components that are not shownin FIG. 8 are well known in the art and are therefore not discussed indetail hereinafter.

The inkjet printer 200 may be a 2D printer or a 3D printer. The printer200 may include one or more processors/controllers 154, a pressurecontrolling system 120 and one or more print heads 130. The pressurecontrolling system 120 is similar in construction and operation to thepressure controlling system 20 of FIG. 2, except that the pressurecontrolling system 120 does not include the internalprocessor/controller 14 of the system 20. The pump 8, the pressurechamber 3, the pressure sensor unit 12 and the valve 4 of the pressurecontrolling system 120 may be configured and may operate in a similarmanner to the operation of the pressure controlling 20, except that theprocessor/controller(s) 154 may be suitably connected to the pump 8 tocontrol the operation of the pump 8. The processor/controller(s) 154 mayalso be connected to the pressure sensor unit 12 to receive therefrompressure related signals and to process the received pressure relatedsignals as disclosed in detail hereinabove with respect to the processorcontroller 14 of the pressure controlling system 20 of FIG. 2. Theprocessor/controller(s) 154 may also be suitably connected to the valve4 for operating (opening and/or closing) the valve 4.

The processor/controller(s) 154 may be also bidirectionally connected tothe print head(s) 130 for sending printing commands to the print head(s)130 and (optionally) for receiving status signals or any other signaloutput by the print head(s) 130. The processor/controller(s) 154 mayalso be connected to an (optional) ink backflow detector 7, similar inconstruction and operation to the ink backflow detector 7 of FIG. 3). Itis, however, noted that the ink backflow detector 7 of the printer 200may or may not be part of the pressure controlling system 120 (in thespecific embodiment illustrated in FIG. 8 the ink backflow detector 7 isnot part of the pressure controlling system and is disposed elsewherewithin the printer 200).

A hollow conduit 260 sealingly fluidically connects the print head(s)130 with the second port 4B of the valve 4. Part of the hollow conduit260 is dispose adjacent to or within the ink backflow detector 7 forsensing and/or detecting ink reaching the part of the hollow conduitassociated with the ink backflow detector 7, as disclosed in detailhereinabove. However, any signals output by the ink backflow detector 7of the printer 200 that indicate that ink backflow has occurred are sentto the processor/controller(s) 154 which may be suitably connected withthe ink backflow detector 7 to receive signals there from.

In accordance with some embodiments of the printer 200 the signals sentby the ink backflow detector 7 may need to be further processed by theprocessor/controller(s) 154 to determine if ink backflow has occurred.In accordance with other embodiments of the printer 200, the inkbackflow detector 7 may have additional detection circuitry (not shownin detail in FIG. 8) included therein which processes any signals sensedand may output a signal representing the occurrence of ink backflow tothe processor/controller(s) 154. If ink backflow has been detected, theprocessor/controller(s) 154 may operate the pump 8 to rapidly increasethe pressure within the pressure chamber 3 (while the valve 4 is open)to purge ink from the hollow conduit 260 and prevent penetration of inkinto any of the components of the pressure controlling system 120, asdisclosed hereinabove in detail with respect to the pressure controllingsystem 30 of FIG. 3.

It is noted that the processor/controller(s) 154 may perform thecontrolling of the operation of the pressure controlling system 120 andmay also perform other functions of the printer 200, such as, forexample, controlling the (2D or 3D) movement of the printing head(s) 130by any moving mechanism (not shown) included in the printer 200,outputting print head commands for ink ejection, performing diagnosticoperations for the printer 200, and may also function to provide a useror operator of the printer with various status data/signals and/orwarnings (such as, for example, controlling a display showing statusdata or the turning on/off of indicator LEDs, and the like), and mayalso be used to receive any commands issued by an operator through ahuman interface (not shown) that may be included in the printer 200.

The processor/controller 154 may also perform any other functionrequired for the operation of any part of the printer 200. Theprocessor/controller(s) 154 may also communicate with an external datasource (such as, but not limited to a personal computer, a laptopcomputer, a remote or a local server, or any other suitable computingand/or data storage device) for receiving data and/or commandsassociated with a printing job to be performed.

It is noted that the pressure levels which need to be reached in thepressure chamber of the pressure controlling systems of the presentapplication (such as, for example, the pressure chambers 2, 3 and 103)may vary in different printers depending, inter alia, on the volume ofthe pressure chamber, the internal volume of the air spaces within theprint head(s) that are fluidically connected to the pressure controllingsystem which may include the volume of any manifold shared by severalprint heads if there is more than one print head in the printer, and thevolume of any hollow conduit connecting the print head or manifold tothe second port (such as, for example the second port 4B or 104B) of thetwo way/three port valve (such as, for example, the valve 4 or the valve104).

Therefore, for each different printer including one of the pressurecontrolling systems disclosed herein, the specific pressure levels thatneed to be reached within the pressure chamber before the two way/threeport valve is opened to perform purging or to achieve the requirednegative pressure level required to avoid weeping needs to be calculatedand/or calibrated in order to program or store these two requiredpressure levels into the memory associated with the processor/controllerof the pressure controlling system (such as, for example, theprocessor/controller 14 or 114), or, in cases in which the pressurecontrolling system does not include a dedicated processor/controllerthereon, into the memory associated with the processor/controlleroperating the printer (such as, for example, the processor/controller154 of the printer 200 of FIG. 8).

Calculation of the Pressure Levels Required for Specific Printers.

The ideal gas law is the equation of state of a hypothetical ideal gas.It is a good approximation of the behavior of many gases and/or gasmixtures under many conditions, although it has several limitations. Theideal gas law is often written as equation (1)

PV=nRT  (1)

Wherein:

P—is the pressure of the gas.

V—is the volume of the gas.

n—is the amount of substance of gas (in moles).

R—is the ideal, or universal, gas constant, equal to the product of theBoltzmann constant and the Avogadro constant.

T—is the absolute temperature of the gas (in degrees Kelvin).

In a closed system by using equation (1) on two volumes including thesame gas the following equation (2) may be derived:

$\begin{matrix}{\frac{PV}{T} = {{C\; \frac{PV}{T}} = C}} & (2)\end{matrix}$

where C is a constant that is directly proportional to the amount of gasn (Avogadro's law). The proportionality factor is the universal gasconstant R.

From equation (2) it is possible to determine the desired purge pressureneeded in a specific printing system.

The system is divided into two separate air compartments. The firstcompartment includes all the volume inside the pressure controllingsystem 100 from the pump pinch (the point at which the peristaltic pumproller pinches the tubing to seal the tubing) to the first solenoid port4A. The second compartment includes all the air volume included in thesecond solenoid port 4B, the tube or conduit connecting the port 4B tothe print head(s) and the volume of air within the internal spaceswithin the print head(s) (including the volume of air within any inkreservoir(s) and all other air spaces within the print head which arefluidically connected with the ink reservoirs). The volume of the firstcompartment is V₁ and the volume of the second compartment is V₂.

Equation (3) will then describe the relation between the two volumes ofthe two compartments in a static manner (when the pump is not working)as derived from equation (2).

$\begin{matrix}{\frac{P_{1}*V_{1}}{T_{1}} = \frac{P_{2}*V_{2}}{T_{2}}} & (3)\end{matrix}$

Once the solenoid valve 104 is open the given combined volume of theentire system is approximately V₃=V₁+V₂ (ignoring any internal volume ofthe solenoid valve 104). The following relation holds:

$\begin{matrix}{\frac{P_{1}*V_{1}}{T_{1}} = {\frac{P_{2}*\left( {V_{2} - V_{1}} \right)}{T_{2}}.}} & a\end{matrix}$

Where,

V₁—is the volume of the pressure reservoir of the printing system.V₂—is constant volume in a specific printing system.P₁—is the preset pressure value that needs to be reached within thepressure chamber of a printer having a pressure reservoir with thevolume V₁ and a second compartment (including the internal volume withinall the printing block(s) of the printer and the internal volume of alltubes or hollow conduits connecting the print head(s) to the solenoidvalve a) having a volume of V₂.T₁—is the air temperature in the first compartment (in degrees Kelvin).T₂—is the air temperature in the second compartment (in degrees Kelvin).

Under normal working conditions, the pressure sensors 112A and 112B (ofFIG. 4) may sense the pressure level in the pressure chamber 103. Thesensing may be continuous or intermittent or may be continuous withdiscrete sampling (and preferably digitizing at a desired frequency).Based on the sensed pressure levels, the processor/controller 114 mayoperate the pump 108 in a suitable rotation direction and at anappropriate speed of rotation to increase or decrease the pressure toreach and/or maintain the pressure values set for various operations ofthe pressure controlling system (such as, for example, the set “purgepressure” and the set “vacuum pressure” disclosed herein).

When a purge sequence is performed, the two compartments are fluidicallydisconnected from each other by the solenoid valve (such as, forexample, the valve 104 of FIG. 5) and the pump (such as, for example,the pump 108 of FIG. 5) is activated to increase the pressure in thefirst compartment.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following examples.

The following Examples 1 and 2 are exemplary calculations:

Example 1

In a printer having two print heads having a known volume V₁ of thefirst compartment and a known volume of the second compartment, thepressure P₁ that needs to be reached in the first compartment (prior toopening the valve, such as the valve 4 of FIGS. 1-3 and 8 or the valve104 of FIG. 4) in order to achieve a given purging pressure P₂ may becalculated as follows:

The total volume of the second compartment (which is the approximatetotal air volume within the two print heads including the volume of anyconduit connecting the print heads to the port 104B of the valve 104) V₂is about 17,300 mm³.

The total volume of the first compartment V₁ (which is the approximatetotal volume of the pressure chamber 103+the volume of the conduitsconnecting the pressure chamber 103 to the port 104A and the volume ofthe conduits connecting the port 108A of the pump 108 to the pressurechamber 103) is about 25,250 mm³

The temperature of the air in the second compartment T2 is about 70° C.(which is about 343K°).

The temperature of the air in the first compartment T1 is about 45° C.(which is about in the 318K°).

The given purging pressure to be reached is P₂=4 PSI

Therefore,

$P_{1} = {{\frac{V_{a}*T_{1}}{V_{1}*T_{2}}*P_{2}} = {{\frac{\left( {17.3 + 25.2} \right)}{25.2}*4} = {6.5\lbrack{PSI}\rbrack}}}$

The above calculation indicates that in order to achieve a purgingpressure P₂ of 4 PSI in the combined volume of the fluidically connectedfirst and second compartments after the valve 104 is opened, thepressure that needs to be achieved within the first compartment by thepump 108 prior to opening the valve 104 is about 6.5 PSI. The abovecalculation gives a result which is approximate only because smallvariations in V₂ may be caused during printer's operation by changes inthe level of ink within the print heads. However, the calculationprovides sufficient accuracy for practically determining the pressure P₂required within the first compartment prior to the opening of the valve104.

Example 2

In a printer having using the same pressure controlling system as inEXAMPLE 1 but having a printing block including eight print heads, thevolume V₁ of the first compartment is like in EXAMPLE 1 above since thefirst compartment is the same. The volume of the second compartment isthe same as in EXAMPLE 1 above since the volume of the pressure chamber103+various attached conduits has not changed (the same pressurecontrolling system is being used), the pressure P₁ that needs to bereached in the first compartment (prior to opening the valve 104) inorder to achieve a given purging pressure P₂ may be calculated asfollows:

V₂ is about is about 54,000 mm³ (as the gas volume of eight print headsis larger than that of two print heads of EXAMPLE 1 above.

V₁ is about 25,250 mm³

The temperature of the air in the second compartment T2 is about 70° C.(which is about 343K°).

The air temperature in the first compartment T1 is about 45° C. (whichis about in the) 318K°.

The given purging pressure to be reached has not changed and is P₂=4 PSI

Using the same equation as in EXAMPLE 1,

$P_{1} = {{\frac{V_{2}*T_{1}}{V_{1}*T_{2}}*P_{2}} = {{\frac{\left( {54 + 25.2} \right)}{25.2}*4} = {12.6\lbrack{PSI}\rbrack}}}$

The pressure P₁ that needs to be reached within the first compartment bythe pump 108 prior to opening the valve 104 in order to reach the samepurging pressure P₂ within all eight printing heads is about 12.6 PSI.

It is noted that, for simplicity of calculation, the pressure valuescalculated in Examples 1 and 2 hereinabove, are calculated using asimplifying assumption that the pump is not operating while a purgesequence is performed. Therefore, the real expected values may be lowersince the pump will actually be operating while the purge sequence isbeing performed. When the pump is activated and the valve is in the openstate, the pressure in the combined volume V₃ is a time dependentfunction.

It will be appreciated that as pressure controlling systems may havedifferent pressure chamber volumes and may be combined with manydifferent types of print heads having various internal volumes, in eachspecific combination of a pressure controlling system and a print head(or print heads) having a specific internal volume the behavior ofpressure as a function of time during a purge sequence and/or duringreturn to vacuum mode may be different. Thus, the value of P₁ may needto be uniquely set and/or calibrated for each such differentcombination.

Reference is now made to FIG. 9 which is a schematic flow chartillustrating the steps of a method of operating the pressure controllingsystem of the present application in a printer, in accordance with someembodiments of the methods of the present application.

The method includes the following steps. The pressure control system(such as, for example, the pressure control system 10, 20, 50, 100, 150and 200) receives from the pressure sensing unit (such as, for example,the pressure sensing unit 12 of FIGS. 1-3 and 8, or the pressure sensors112A and/or 112B of FIG. 4) pressure related signals representing thepressure level within the pressure chamber (such as, for example, thepressure chamber 2 of FIG. 1, or the pressure chamber 3 of FIGS. 2-3 and8, or the pressure chamber of FIGS. 4-6), in step 202.

The pressure control system may also receive printing control signalsfor operating the print head (step 204). Typically, the printing controlsignals may be sent from a separate processor/controller which controlsthe operation of the printer (such as, for example, the processorcontroller 24 of FIG. 3 or any printer controllingprocessor/controller(s) connected to the communication line 15 of FIGS.1-3). However, in some embodiments of the pressure control system of thepresent application, in which a single processor/controller controls allthe different functions and operations of the printer, including theoperation of the pressure controlling system (such as, for example, theprocessor/controller 154 of the printer 200 of FIG. 8), In such a case,the receiving printer control signals of step 204 may mean that thesoftware program(s) operating on the common printer processor/controller(such as, for example the processor controller 154) may actuallygenerate the printing control signals and need not receive them fromanother processor, and the terms “receiving printing control signals”may mean that a software subroutine or program software modulecontrolling the operation of the pressure control system receivesprinting control signals from the main program or from anothersubroutine or program software module that may control the printingfunctions of the printer. Thus, the term “receiving printing controlsignals” may in this case mean “internally” receiving or having accessto such signals generated within the same single processor/controller.

The pressure control system may then process the pressure relatedsignals and the printing control signals to provide pump control signalsfor controlling the speed and/or the direction of pumping of the pump(such as for example, the pump 8 of FIGS. 1, 2, 3 and 8 or the pump 108of FIG. 4) and valve control signals for controlling the operation ofthe valve (such as, for example, the valve 4 of FIGS. 1, 2, 3 and 8, orthe valve 104 of FIG. 4) in step 206. As disclosed in detailhereinabove, the valve has two states, an open state and a closed state.If the valve is a normally open valve, a control signal for closing thevalve may be a positive voltage signal such as a positive voltage pulseapplied to the valve control terminals and a control signal for openinga closed valve may be a return of the voltage signal to zero or to apositive voltage lower than the positive voltage value required foropening the valve. However, the signals may be other different signalsdepending on the specific type of valve being used as is well known inthe art.

Similarly, if the valve is a normally closed valve, the valve controlsignals may be a control signal for opening the valve may be a positivevoltage signal such as a positive voltage pulse applied to the valvecontrol terminals and a control signal for closing an open valve may bea return of the voltage signal to zero or to a positive voltage lowerthan the positive voltage value required for opening the valve. However,the signals may be other different signals depending on the specifictype of valve being used as is well known in the art.

Reference is now made to FIGS. 10A-10B which are schematic flow chartsillustrating the steps of a method of operating a pressure controllingsystem in a printer, in accordance with some embodiments of the methodsof the present application.

The flow chart of FIGS. 10A-10B is a specific example of animplementation of the method for operating the pressure controllingsystem 100 of FIGS. 4-6 in conjunction with a specific inkjet print head(not shown).

The program operating on the pressure controlling system 100 may startfrom a state in which the pump 108 is idle (at rest) and the valve 104is open (step 250). The program checks whether a vacuum mode command isdetected (step 252). If a vacuum mode command is detected, the programchecks if liquid (ink) backflow has been detected (such as, for example,by the ink backflow detector 7 of FIGS. 3 and 8), in step 254. If inkbackflow has been detected, the program operates the pump 108 at mediumspeed in a positive rotation direction (as indicated by the “+” sign) toincrease the pressure within the pressure chamber 108 and within theprint head fluidically connected to the valve 106 for at time period ofT1 seconds (step 256), waits for a time period of T2 seconds withoutpumping (step 258), operates the pump 108 again in a positive (+)rotation direction at medium speed for a time period of T3 seconds (step260) and disables the pump 108 (step 262). Optionally, the program mayalso issue a backflow warning or message (step 264) to indicate to auser that backflow has occurred. At step 264, preferably, when the pumpis disabled, printing is stopped and the printer cannot be reactivateduntil the backflow issue is resolved.

In step 254, if ink backflow has not been detected, the program proceedsby checking if the value of a “purge phase 1” flag equals 1, indicatingthat a print head purge is required (step 266). If purge phase 1 flag=1,the program closes the valve 104 (step 268) and operates the pump 108 ata medium speed in a negative rotation direction (as indicated by the “−”sign) to lower the pressure within the pressure chamber 103 (step 270).The program then checks if the pressure level in the chamber 103 isgreater than or equal to a set vacuum pressure level (step 272). If thepressure level in the chamber 103 is greater than or equal to the vacuumpressure level, the program continues to operate the pump 108 byreturning control to step 272, to further decrease the pressure in thepressure chamber 103. The “vacuum pressure level” is a set or preset orprogrammed pressure value which is determined by the volume of thespecific print head(s) fluidically coupled to the pressure controllingsystem, as explained in detail in Examples 1 and 2 hereinabove.

If the pressure level in the chamber 103 is smaller than the set vacuumpressure level, the program opens the valve 103 to allow the pressurewithin the print head(s) to decrease to the desired vacuum mode pressureas explained in detail hereinabove (step 274), sets the value of thephase 1 flag to one (step 276) and returns control to step 250.

In step 266, if the phase 1 purge flag is not equal to one, the programchecks if the pressure level in the chamber 103 is larger than the setvacuum pressure level (step 278). The “vacuum pressure level” value is aset or preset or programmed pressure value that is determined by thevolume of the specific print head which is fluidically coupled to thepressure controlling system, as explained in detail in Examples 1 and 2hereinabove). If the pressure level in the pressure chamber 103 islarger than the vacuum pressure level, the program operates the pump ata medium speed in a negative (−) rotation direction to further reducethe pressure in the vacuum chamber 103 (step 280) and transfers controlto step 278.

If the pressure level in the chamber 103 is not larger than the vacuumpressure level, the program checks whether the pressure level in thepressure chamber 103 is smaller than the vacuum pressure level (step282).

If the pressure level in the pressure chamber 103 is smaller than thevacuum pressure level, the program operates the pump 108 at low speed ina positive rotation direction to increase the pressure level in thepressure chamber 103 (step 284) and returns control to step 282. If thepressure level in the pressure chamber 103 is not smaller than thevacuum pressure level, the program transfers control to step 250.

In step 252 (of FIG. 10A), if a vacuum mode command has not beendetected, the program checks if purge phase 1 flag=1 (step 286). Ifpurge phase 1 flag=1, the program checks if the pressure level in thepressure chamber 103 is equal to or larger than the purge pressure level(step 288). If purge phase 1 flag=1, the program transfers control tostep 250. If the value of purge phase 1 flag is not equal to 1, theprogram operates the pump 108 at medium speed in a positive rotationdirection (+) to increase the pressure level within the pressure chamber103 (step 290) and transfers control to step 288.

In step 286, if the Purge Phase 1 flag is not equal to one, the programscloses the valve 104 (step 292), operates the pump 108 at maximum speedin a positive (+) rotation direction (step 294) and checks if thepressure level in the pressure chamber 103 is larger than or equal tothe purge pressure level (step 296). If the pressure level in thepressure chamber 103 is not larger than or equal to the purge pressurelevel, the program returns control to step 294 to continue operating thepump 108. If the pressure level in the pressure chamber 103 is largerthan or equal to the purge pressure level, the program opens the valve104 and sets phase 1 flag=1 (step 298) and then transfers control tostep 250.

It is noted that in accordance with a specific exemplary embodiment ofthe method of FIGS. 10A-10B, the time intervals T1, T2 and T3 (of steps256, 258 and 260, respectively) have the following values: T1=5 seconds,T2=30 seconds, and T3=15 seconds. While these specific values of thetime intervals T1, T2 and T3, were found to be adequate for properoperation of the pressure controlling system 100 when it is fluidicallyconnected with a specific print block with parameters as disclosed inEXAMPLE 1 hereinabove, these specific values are by no means obligatoryto practicing the method and it should be realized that other differentvalues of T1, T2 and T3 (lower and/or higher than the specific valuesgiven in the particular example disclosed herein) may be used in theprogram, depending, inter alia, on the print head(s) or print block(s)being used in conjunction with the pressure controlling system, thepump's, pumping capacity and other considerations. Adequate values forthese parameters may be easily determined empirically by the personskilled in the art without undue experimentation.

It is further noted that for the specific peristaltic pump (the modelWP11-N1/4(200)BA2G-BS material peristaltic pump) used in one specificexemplary embodiment of the vacuum controlling system 100 as disclosedhereinabove, the following pump speed ranges were found to be suitablefor operation of the program when the pressure controlling system 10 wasfluidically connected to a print head having the same volume andpressure parameters as disclosed in EXAMPLE 1 hereinabove:

Low Speed=0.3-0.4 RPS.

Medium speed=1.0-1.5 RPS.

High Speed=2.3-2.5 RPS.

However, these pump speed ranges are given by way of example only, arenot obligatory, and may vary depending, inter alia, on the volume of thefirst compartment of the system being used, the total internal volumewithin the print head(s) being used (the second compartment volume), andthe pumping capacity and other characteristics of the specific pumpbeing used in the pressure controlling system.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention. To theextent that section headings are used, they should not be construed asnecessarily limiting.

1. A pressure controlling system for an inkjet printer, the systemcomprising: a pressure chamber having a volume; a pump fluidicallyconnected to said pressure chamber and adapted for increasing thepressure within said pressure chamber by pumping air into said pressurechamber and for decreasing the pressure within said pressure chamber bypumping air out of said pressure chamber; a controllable three port twoway valve having a first port controllably fluidically connectable tosaid pressure chamber, a second port controllably fluidicallyconnectable to one or more inkjet print heads and a third portcontrollably fluidically connectable with atmospheric air; and apressure sensor unit comprising one or more pressure sensors, saidpressure sensor unit is in fluidic communication with said pressurechamber for sensing the pressure within said pressure chamber; whereinsaid pressure sensor unit is adapted for sending signals representativeof the pressure within said pressure chamber to at least oneprocessor/controller, and wherein said pump is adapted to receivecontrol signals from said at least one processor/controller forcontrolling the operation of said pump and said valve is adapted forreceiving control signals from said at least one processor/controllerfor controlling the operation of said valve.
 2. The pressure controllingsystem according to claim 1, wherein said at least oneprocessor/controller unit is selected from: at least oneprocessor/controller included in said pressure controlling system andadapted to control the operation of said valve and of said pump, said atleast one processor/controller is also adapted to communicate with atleast a second processor/controller controlling the operation of one ormore print heads of said printer for receiving command signals from saidat least a second processor/controller, at least oneprocessor/controller included in said printer and adapted to control theoperation of said pressure controlling system and for controlling theoperation of said one or more print heads of said printer, and acombination of at least one processor/controller included in saidpressure controlling system and at least one processor/controllerincluded in said printer and communicating with said at least oneprocessor/controller of said pressure controlling system, saidcombination is adapted for operating said pump and said valve and forcontrolling the operation of said one or more print heads of saidprinter.
 3. The pressure controlling system according to claim 1,wherein the pressure controlling system also includes a filterfluidically connected between said pump and the atmospheric air forfiltering air entering said pump.
 4. The pressure controlling systemaccording to claim 1, wherein said second port of said valve isfluidically connected to said one or more inkjet print heads by One ormore hollow conduits for controlling the pressure within said one ormore print heads and wherein said pressure controlling system alsoincludes an ink backflow detecting sensor for detecting backflow of inkfrom said one or more inkjet print heads through one or more hollowconduits before said ink enters said second port.
 5. The pressurecontrolling system according to claim 4, wherein said one or more hollowconduits are transparent hollow conduits and wherein said ink backflowdetecting sensor is an optical sensor.
 6. The pressure controllingsystem according to claim 1, wherein said pump is a reversibleperistaltic pump.
 7. The pressure controlling system according to claim1, wherein said pump includes a stepper motor.
 8. The pressurecontrolling system according to claim 1, wherein said pressure sensingunit is selected from: a pressure sensing unit disposed within saidpressure chamber, and a pressure sensing unit disposed outside saidpressure chamber and fluidically connected to said pressure chamberthrough one or more hollow conduits connected to said one or morepressure sensors.
 9. The pressure controlling system according to claim1, wherein said pressure sensing unit comprises multiple pressuresensors, each pressure sensor of said multiple pressure sensors isadapted for sensing pressure is a sub-range of the full range ofpressures achievable within said pressure chamber for increasing thedynamic range and/or the resolution of said pressure sensing unit. 10.The pressure controlling system according to claim 1, wherein said threeport two way valve is a solenoid valve.
 11. An inkjet printer, theprinter comprising: the pressure controlling system according to claim1; and at least one controllably movable inkjet print head, said atleast one print head is fluidically connected to said pressurecontrolling system for controlling the pressure level within at leastone internal ink reservoir disposed within said at least one print head.12. The printer according to claim 11, wherein said at least oneprocessor/controller unit is selected from: at least oneprocessor/controller included in said pressure controlling system andadapted to control the operation of said valve and of said pump, said atleast one processor/controller is also adapted to communicate with atleast a second processor/controller controlling the operation of atleast one print head of said printer, for receiving command signals fromsaid at least a second processor/controller, at least oneprocessor/controller included in said printer and adapted to control theoperation of said pressure controlling system and for controlling theoperation of said at least one print head of said printer, and acombination of at least one processor/controller included in saidpressure controlling system and at least one processor/controllerincluded in said printer and communicating with said at least oneprocessor/controller of said pressure controlling system, saidcombination is adapted for operating said pump and said valve and forcontrolling the operation of said at least one print head of saidprinter.
 13. The printer according to claim 11, wherein the pressurecontrolling system also includes a filter fluidically connected betweensaid pump and the atmospheric air for filtering air entering said pump.14. The printer according to claim 11, wherein said second port of saidvalve is fluidically connected to said at least one inkjet print head bya hollow conduit for controlling the pressure within said at least oneprint head and wherein said pressure controlling system also includes anink backflow detecting sensor for detecting backflow of ink from said atleast one inkjet print head through said hollow conduit before to saidink enters said second port.
 15. The printer according to claim 14,wherein said hollow conduit is a transparent hollow conduit and whereinsaid ink backflow detecting sensor is an optical sensor.
 16. The printeraccording to claim 11, wherein said pump is a reversible peristalticpump.
 17. The printer according to claim 11, wherein said pump includesa stepper motor.
 18. The printer according to claim 11, wherein saidpressure sensor unit is selected from: a pressure sensor unit disposedwithin said pressure chamber, and a pressure sensor unit disposedoutside said pressure chamber and fluidically connected to said pressurechamber through one or more hollow conduits connected to said one ormore pressure sensors.
 19. The printer according to claim 11, whereinsaid pressure sensor unit comprises multiple pressure sensors, eachpressure sensor of said multiple pressure sensors is adapted for sensingpressure is a sub-range of the full range of pressures achievable withinsaid pressure chamber for increasing the dynamic range and/or theresolution of said pressure sensing unit.
 20. The printer according toclaim 11, wherein said three port two way valve is a solenoid valve. 21.The printer according to claim 11, wherein said ink jet printer isselected from a 2D inkjet printer and a 3D inkjet printer.
 22. A methodfor controlling pressure in a print head of an inkjet printer comprisingthe pressure controlling system according to claim 1, the methodcomprises the steps of: receiving pressure related signals from saidpressure sensing unit of said pressure controlling system, said pressurerelated signals represent the pressure level within said pressurechamber; receiving printing control signals for operating said printhead; processing said pressure related signals and/or said controlsignals to provide pump control signals to said pump and/or valvecontrol signals to said valve.
 23. The method according to claim 22,wherein said step of processing comprises the steps of: receiving avacuum mode control signal, closing said valve to fluidically connectsaid print head to the atmosphere and to disconnect said pressurechamber from the atmosphere, operating said pump to reduce the pressurewithin said pressure chamber to a vacuum mode pressure level, andopening said valve to fluidically connect said print head to saidpressure chamber.
 24. The method according to claim 23, wherein saidvacuum mode pressure level is a set or preset pressure level.
 25. Themethod according to claim 22, wherein said step of operating said pumpcomprises the step of closing said valve to allow the pressure withinsaid pressure chamber to equilibrate with atmospheric pressure prior tosaid step of operating said pump.
 26. The method according to claim 22,wherein said step of processing comprises: receiving a purging controlsignal for performing purging of said print head, closing said valve toallow the pressure within said print head to equilibrate withatmospheric pressure, operating said pump to increase the pressurewithin said pressure chamber to a purge pressure level, and opening saidvalve to fluidically disconnect said print head from the atmosphere andto fluidically connect said pressure chamber to said print head, forpurging said print head.
 27. The method according to claim 26, whereinsaid purge pressure level is a set or preset value.
 28. The methodaccording to claim 26, wherein said step of processing also comprisesreversing the direction of pumping of said pump after said purging iscompleted to reduce the pressure within said pressure chamber to a levelequal to or smaller than a vacuum mode pressure level.
 29. The methodaccording to claim 22, wherein said step of processing also comprisesthe step of checking if ink backflow is detected and if ink backflow hasbeen detected operating said pump to increase pressure within saidpressure chamber for preventing ink from entering said pressurecontrolling system.
 30. The method according to claim 29, wherein saidstep of checking also includes the step of disabling said pump aftersaid preventing.
 31. The method according to claim 30, wherein said stepof checking also includes the step of outputting an ink backflowmessage.